org.lwes.listener.ThreadedEventDispatcher.java Source code

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Here is the source code for org.lwes.listener.ThreadedEventDispatcher.java

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/*======================================================================*
 * Copyright (c) 2008, Yahoo! Inc. All rights reserved.                 *
 *                                                                      *
 * Licensed under the New BSD License (the "License"); you may not use  *
 * this file except in compliance with the License.  Unless required    *
 * by applicable law or agreed to in writing, software distributed      *
 * under the License is distributed on an "AS IS" BASIS, WITHOUT        *
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.     *
 * See the License for the specific language governing permissions and  *
 * limitations under the License. See accompanying LICENSE file.        *
 *======================================================================*/

package org.lwes.listener;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.lwes.Event;

/**
 * Dispatches events to downstream handlers using threads.
 * @author Preston Pfarner
 * @author Michael P. Lum
 */
public class ThreadedEventDispatcher extends Thread {

    private static transient Log log = LogFactory.getLog(ThreadedEventDispatcher.class);

    /* dequeuer controlling this object */
    private ThreadedDequeuer dequeuer;
    private EventHandler eventHandler;
    private Event event;

    protected ThreadedEventDispatcher(ThreadedDequeuer aDequeuer) {
        this.dequeuer = aDequeuer;
        super.start();
        setName("EventDispatcher");
    }

    public void setTask(EventHandler aHandler, Event anEvent) throws IllegalStateException {
        if (isIdle()) {
            synchronized (this) {
                eventHandler = aHandler;
                event = anEvent;
            }
            synchronized (this) {
                notifyAll();
            }
        } else {
            throw new IllegalStateException("Processor already has a listener");
        }
    }

    public final boolean isActive() {
        return (!isIdle());
    }

    public final boolean isIdle() {
        final boolean p1 = (eventHandler == null);
        final boolean p2 = (event == null);
        if (p1 == p2)
            return p1;
        else
            throw new IllegalStateException("Contradictory state indication");
    }

    @Override
    public void run() {
        while (true) {
            synchronized (this) {
                if (isActive()) {
                    try {
                        eventHandler.handleEvent(event);
                    } catch (Exception e) {
                        log.warn("Caught exception handling event", e);
                    }
                    clearTask();
                } else {
                    try {
                        wait();
                    } catch (InterruptedException e) {
                    }
                }
            }
        }
    }

    private void clearTask() {
        synchronized (this) {
            eventHandler = null;
            event = null;
        }

        dequeuer.makeAvailable(this);
    }

}